1. Field of the Invention
The present invention concerns a method and devices for the transmission of data for quadrature amplitude modulation.
It applies to the transmission of data over any transmission channel using this modulation.
2. Description of the Related Art
Quadrature amplitude modulation of signals is well known in the communications field. According to this modulation technique, there is associated with data to be transmitted a signal which is of constant frequency but whose amplitude and phase represent the data.
However, on reception, these signals may sometimes be difficult to identify if, during transmission, the signal has been distorted.
In addition, the spectrum of these signals may be relatively narrow compared with the spectrum available for transmission. This gives rise to known drawbacks. By way of example, two of these drawbacks are mentioned below:
when the energy of the signals is concentrated in an excessively narrow spectrum, these signals are easily detected and interfered with by enemies; PA1 for some applications, regulations require the energy of the signals to be distributed sufficiently over the entire frequency band available. PA1 the signals are more difficult to detect and to interfere with; PA1 the distribution of energy over the available frequency band is improved; PA1 the resistance of the signals to unintentional noise is increased. PA1 the combination means is adapted to locate each periodic signal phase and amplitude pair by means of a pair of figures (a,b), each term of which is an integer between zero and n-1 inclusive; PA1 the combination means is adapted to calculate the function of combination of the pairs, for each of the terms, modulo n; PA1 the combination means is adapted to associate the pair (a.sub.1.a.sub.2 +(n-1).b.sub.1 b.sub.2, b.sub.1 a.sub.2 +b.sub.2 a.sub.1 +(n-1) .b.sub.1 b.sub.2) with two pairs (a.sub.1, b.sub.1) and (a.sub.2, b.sub.2), each addition being performed modulo n; PA1 the number n is equal to 8, and with each pair the combination means associates the result of the function of combination of the pair with a constant pair whose period is 12.
The invention sets out to remedy these drawbacks by proposing a method and devices for data transmission having the following advantages: